1. Field of the Invention
The present invention relates generally to a cleaning process for oxide, and more specifically to a cleaning process performed on a gate oxide in an input/output area as well as a core area.
2. Description of the Prior Art
With advances in semiconductor technology, integrated circuits (IC′) that have multi-functional circuit modules composed of a large number of transistors and/or other semiconductor devices integrated on a silicon die have become ever more popular. In integrated circuits of VLSI and ULSI, the number of transistors and/or other semiconductor devices included is huge and the devices are densely packed together. Therefore, there are isolation structures between adjacent transistors/devices to prevent short circuits from occurring. The most commonly used isolation structures may include field oxide isolation, and trench isolation such as shallow trench isolation (STI). When the line width of the semiconductor device falls to below 0.25 μm, isolating devices using a field oxide layer becomes infeasible and trench isolation becomes the only means of device isolation.
Moreover, in an integrated circuit, different circuit modules and/or transistors and other devices in the same chip may operate in different voltage regimes. In an integrated switching-mode power supply, which may include a power transistor and a control circuit for switching the power transistor ON and OFF to convert a supply voltage into a desired output voltage, the power transistor may have an operating voltage much higher than an operating voltage of transistors constituting the control circuit. In order to have an area-efficient high voltage device with low voltage control devices fabricated on a same die, gate insulation layers with different thicknesses are required. When the high-voltage driving elements and the low-voltage driving elements are embodied simultaneously, a thick gate oxide film for high voltage and a thin gate oxide film for low voltage are required.